1. Field of the Invention
The invention relates to a display apparatus, and more particularly, to a projection apparatus.
2. Description of the Related Art
A field lens for a projection apparatus is disclosed in a number of patents such as U.S. Pat. No. 6,273,568, US patent No. 2007/0279602, US patent No. 2007/0273979, U.S. Pat. No. 6,888,682, Taiwanese patent No. 494270, and Taiwanese patent No. 457396. The field lens is configured for reducing an incident angle of an illumination light beam which is incident to a light valve to prevent the light valve from being overfilled by the illumination light beam and thereby improving light utility efficiency. Moreover, with a filed lens, a projection lens could have shorter back focal length, which is able to be used in the projection apparatus and the size of the projection apparatus could be reduced thereby.
However, when a transmittance of the field lens is less than 100%, a portion of the illumination light beam may be reflected by the field lens. The reflected light beam (i.e. stray light beam) reflected from the field lens may be reflected to the projection lens and then be projected on a screen, and therefore a ghost image is displayed on the screen. The ghost image reduces display quality of the projection apparatus, so that it is important to reduce the ghost image.
Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention.